Enteral adenoviruses are a recently discovered group of agents which cause gastroenteritis in infants. They differ from all other known human adenoviruses in their inability to be propagated in tissue culture. During the past year we have continued to obtain specimens from sources around the world. Stool specimens have been characterized by enzyme immunoassay, electronmicroscopy and propagation in tissue culture. These agents have been studied extensively to determine the biological basis for their inability to grow in tissue culture. We have learned that these agents induce an abortive infection which is abruptly terminated at a very early step of the virus growth cycle in vitro. Using these findings, we have developed a successful strategy to complement the block to the virus replication and succeed for the first time in permitting the efficient replication of these viruses in cell culture. Enteral adenoviruses grown in culture for the first time have now been analyzed and characterized extensively in terms of their polypeptides, the structure of the genomes, and their antigenicity.